Transcranial magnetic stimulation (TMS) is a non-invasive technique to directly and focally modify brain function by inducing electrical currents in neural tissue. Its use as an experimental technique to study human neurophysiology has gained in popularity as more paradigms are being discovered where TMS can be used to affect neural and behavioral responses. More importantly, researchers have begun to suspect that TMS may be useful in the treatment of brain disorders such as depression, Parkinson's disease, and dystonia. Despite this research, almost nothing is known about how much tissue TMS affects, or about the mechanisms of its action. We propose to study the effects of TMS directly in an animal model using modern techniques of neural recording and brain imaging. These techniques include recording activity in single neurons, visualization of activity-dependent glucose (2-DG) uptake in tissue, and visualization of activity-related changes in bloodflow using intrinsic signal imaging. We will ask (1) does TMS have the same effect on cortical tissue regardless of the state of cortical activity, and can it be used to modify activity-dependent processes? (2) What are the long-term effects of TMS, and does varying the frequency of repetitive stimulation change its long-term effect? (3) Can TMS alter function trans-synaptically, when applied over an area in which a transient lesion is known to affect visual cortex. The short-term goal of these studies is to develop TMS as a useful tool for probing the neural circuitry underlying visual function. The long-term goal is to better understand how TMS can be used to modify visual function, modify cortical function in general, and treat neurological disease states in humans.